Our hosting provider backs up all our Drupal databses automatically for the past three days. We can also schedule a manual backup of the database whenever we want. Manual backups are not deleted but automatic backups just stay for 3 days.
SF State Drupal sites have revisions turned on by default for all the nodes (pages). These revisions are different from the backups. All the changes ever made on each page is stored in revisions for that page. One can easily compare changes between revisions and can revert to any version. The screenshot shows a typical revisions listing for a page.
Revisions help store the history of every page however they don't store Menu items, sidebar blocks and views. Full databse backups are required for that.
There are additional functions in the Revisioning module that lets one create a publishing workflow and moderations. This post just explains the basic revisioning.